1. Field of the Invention
The present invention relates to a textured metal substrate for forming an epitaxial thin film thereon and a method for manufacturing the same, and specifically relates to a textured metal substrate which is provided with a silver layer having a predetermined orientational structure, can make the thin film of high quality epitaxially grown thereon, and has a reliable strength, and a method for manufacturing the same.
2. Description of the Related Art
In recent years, a thin film produced while paying attention to characteristics of an epitaxial crystal structure is used in various fields. For instance, a superconducting thin film (formed of oxide superconducting material) having the epitaxial crystal structure is used in a superconducting conductor, a superconducting shield and the like, which are applied to various electric power units. However, the superconducting thin film having such an epitaxial crystal structure is inferior in workability, and has a defect of being hardly molded into a desired shape. For this reason, a superconductor of a shape suitable for a field of application is conventionally obtained by appropriately employing a necessary substrate for applying a superconducting material thereon, and epitaxially growing the superconducting film on the surface.
As such a substrate for forming an epitaxial thin film thereon, a clad textured metal substrate is used which has a {100}<001> cube texture employs and is made from silver or a silver alloy (for instance, “Control of texture in Ag and Ag-alloy substrates for superconducting tapes” by T A Gladstone, J C Moore, B M Henry, S Speller, C J Salter, A J Wilkinson and C R M Grovenor, Department of Materials, University of Oxford, Supecond. Sci. Techno. 13(2000) 1399-1407, printed in the UK). Characteristics of a epitaxial thin film are affected by the orientation of composing crystals, and the crystal structure formed through epitaxial growth is affected by the orientation of the surface of the substrate. A substrate having excellent orientation can be easily obtained by appropriately adding working and heat treatment (recrystallization) to a silver-based metallic material.
However, a textured metal substrate for forming an epitaxial thin film made from the above described silver-based material has several problems. Particularly, a problem of the strength is pointed out. This is because the crystal structure of the textured metal substrate is formed basically by recrystallization, and a metal having a recrystallized structure cannot help decreasing the strength, which is general characteristics of a metallic material. It is hard to handle the substrate having poor strength when forming an epitaxial thin film thereon, because the substrate may be damaged.
In addition, a conventional silver-based substrate has not had a satisfactory orientational structure even though having it. The orientation of a substrate greatly affects the characteristics of the epitaxial thin film formed thereon, so that the substrate is required to have an orientation as adequate as possible.
The present invention has been accomplished based on the above described background, and is directed at providing the oriented substrate for forming an epitaxial thin film thereon which has a better orientation than that of a conventional one and a high strength, and a method for manufacturing the same.